In many industries, it may be necessary to send tooling through a tubular component such as a pipe, for example for pipeline inspection, cleaning, testing, isolation and the like. In the oil and gas industry, one way of transporting tooling through a pipe is via a pig or pigging tool. A pigging tool is a device that can be located within a pipe and transported through the pipe by fluid flow. Typically, a seal is generated between the pigging tool and the pipe wall in order that the pressure force from the pipe flow can be used to propel the tool through the pipe.
In solid body pigging tools, for example, one system for generating a seal is to use a pre-formed cup disc seal arrangement. The seal includes a pre-formed cup shaped seal member that is coupled to the pigging tool body. In use, upstream pressure within the pipe deforms the seal cup, thereby pushing the outer lip of the seal into engagement with the pipe wall.
An alternative system uses one or more substantially planar discs coupled to the pigging tool body. The discs are typically constructed from a polymeric material, such as polyurethane, and are of larger outer diameter than the pipe internal diameter. The discs are deflected into the desired cup shape as the tool is inserted into the pipe. In use, the profile of the deformed discs may be reversed, or flipped, when the flow in the pipe is reversed, thus facilitating operation of the tool in forward and reverse directions.
In general, the choice of system adopted depends on the operational requirements of the tool. For example, the pre-formed cup disc system is most suitable for use in performing pigging operations under higher pressure pipe flow conditions, the higher pressure facilitating the transport of heavier payloads on the pigging tool. However, the internal surface of a pipe may be non-uniform, and it is known that the lip of the pre-formed cup is susceptible to snagging in the pipe, this preventing the pigging tool from operation in a reverse direction. Where the tool encounters an impassable obstruction in the pipe, this can represent a significant problem. Typically, where an obstruction is encountered in the pipe, which prevents passage of the pigging tool, the flow in the pipe is reversed to dislodge or otherwise facilitate removal of the obstruction or the tool from the pipe. However, reversal of the pressure on the pre-formed cup disc acts to apply pressure to the outside of the cup, which tends to push the cup away from the pipe inner wall, thereby causing bypass of the seal. Thus, flow reversal may not be suitable to facilitate recovery of the tool.
The planar disc seal system has the advantage that it is capable of effective operation in more than one direction. However, substantial force is required to insert the tool into a pipe due to the requirement to deflect the discs during insertion. Furthermore, deflection of the discs applies a significant load onto the outer edge of the discs resulting in wear and reduced operational life of the tool. The disc seal system is also known to be less compliant to changes and/or variations in pipe inner diameter than, for example, the pre-formed cup disc system. Moreover, in use, where the pressure on the tool exceeds the load required to flip the discs, the discs may involuntarily invert. This may reduce the pressure retaining capability of the tool and may cause the tool to stall.
Where a tool has stalled in the pipe, this may be overcome by inverting the flow direction in the pipe to move the tool in a reverse direction. However, the orientation of the discs may only be reversed or flipped back where sufficient differential pressure can be applied to the tool by the reverse flow.